U.S. patent application number 12/651838 was filed with the patent office on 2010-07-08 for hearability improvements for reference signals.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Avneesh Agrawal, Raja Sekhar Bachu, Naga Bhushan, Aamod D. Khandekar, Ravi Palanki, Ashwin Sampath.
Application Number | 20100172311 12/651838 |
Document ID | / |
Family ID | 42311654 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172311 |
Kind Code |
A1 |
Agrawal; Avneesh ; et
al. |
July 8, 2010 |
HEARABILITY IMPROVEMENTS FOR REFERENCE SIGNALS
Abstract
Systems and methodologies are described that facilitate
providing high reuse for transmitting reference signals, such as
positioning reference signals (PRS) and cell-specific reference
signals (CRS), to improve hearability thereof for applications such
as trilateration and/or the like. In particular, PRSs can be
transmitted in designated or selected positioning subframes.
Resource elements within the positioning subframe can be selected
for transmitting the PRSs and can avoid conflict with designated
control regions, resource elements used for transmitting
cell-specific reference signals, and/or the like. Resource elements
for transmitting PRSs can be selected according to a planned or
pseudo-random reuse scheme. In addition, a transmit diversity
scheme can be applied to the PRSs to minimize impact of introducing
the PRSs to legacy devices. Moreover, portions of a subframe not
designated for PRS transmission can be utilized for user plane data
transmission.
Inventors: |
Agrawal; Avneesh; (San
Diego, CA) ; Sampath; Ashwin; (Skillman, NJ) ;
Palanki; Ravi; (San Diego, CA) ; Bhushan; Naga;
(San Diego, CA) ; Bachu; Raja Sekhar; (Somerset,
NJ) ; Khandekar; Aamod D.; (San Diego, CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
42311654 |
Appl. No.: |
12/651838 |
Filed: |
January 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61142784 |
Jan 6, 2009 |
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61144075 |
Jan 12, 2009 |
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61149647 |
Feb 3, 2009 |
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61151128 |
Feb 9, 2009 |
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61163429 |
Mar 25, 2009 |
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Current U.S.
Class: |
370/329 ;
375/260 |
Current CPC
Class: |
H04L 1/1893 20130101;
H04L 5/0048 20130101; H04W 72/005 20130101; H04L 5/005 20130101;
H04L 5/0082 20130101; H04W 72/1247 20130101 |
Class at
Publication: |
370/329 ;
375/260 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Claims
1. A method, comprising: determining a positioning subframe
configured for transmitting positioning reference signals (PRS);
selecting one or more resource elements in the positioning subframe
for transmitting a PRS avoiding resource elements in the
positioning subframe configured for transmitting cell-specific
reference signals (CRS); and transmitting a PRS in the one or more
resource elements.
2. The method of claim 1, wherein the selecting one or more
resource elements includes selecting the one or more resource
elements in a portion of the positioning subframe.
3. The method of claim 2, wherein the selecting one or more
resource elements in the portion of the positioning subframe
includes selecting the one or more resource elements in a slot of
the positioning subframe.
4. The method of claim 3, wherein the slot of the positioning
subframe is adjacent to a disparate slot of the positioning
subframe that includes a set of resource elements reserved for
transmitting control data.
5. The method of claim 3, wherein the selecting one or more
resource elements includes selecting the one or more resource
elements in consecutive orthogonal frequency division multiplexing
(OFDM) symbols in the slot of the positioning subframe.
6. The method of claim 5, wherein the selecting one or more
resource elements in consecutive OFDM symbols includes shifting
between subcarriers of the consecutive OFDM symbols.
7. The method of claim 6, wherein the shifting between subcarriers
of the consecutive OFDM symbols includes shifting between
subcarriers of the consecutive OFDM symbols according to a diagonal
pattern.
8. The method of claim 3, wherein the selecting one or more
resource elements includes selecting the one or more resource
elements to have a similar periodicity and a similar structure as
CRSs.
9. The method of claim 1, wherein the selecting one or more
resource elements includes selecting the one or more resource
elements according to a planned selection function or a
pseudo-random selection function.
10. The method of claim 1, wherein the selecting one or more
resource elements in the positioning subframe for transmitting the
PRS further includes avoiding a portion of the positioning subframe
allocated for control data transmissions.
11. The method of claim 1, further comprising applying a transmit
diversity scheme to the PRS.
12. The method of claim 11, wherein the transmitting the PRS is
performed over a single antenna port utilized to transmit remaining
PRSs in the positioning subframe.
13. The method of claim 1, wherein the selecting one or more
resource elements in the positioning subframe includes selecting
the one or more resource elements from a subband, comprising a
plurality of consecutive resource blocks, related to transmitting
the PRS according to a network specification or a
configuration.
14. The method of claim 1, further comprising indicating that the
positioning subframe is a multicast/broadcast single frequency
network subframe.
15. The method of claim 1, wherein the transmitting the PRS in the
one or more resource elements includes transmitting the PRS
according to a Zadoff-Chu sequence, a Walsh sequence, or a
quadrature phase-shift keying sequence to ease detection of the
PRS.
16. A wireless communications apparatus, comprising: at least one
processor configured to: select a portion of a positioning subframe
for transmitting positioning reference signals (PRS); determine one
or more resource elements in the positioning subframe, excluding a
plurality of disparate resource elements allocated for transmitting
cell-specific reference signals (CRS), for transmitting a PRS; and
transmit the PRS in the one or more resource elements; and a memory
coupled to the at least one processor.
17. The wireless communications apparatus of claim 16, wherein the
portion of the positioning subframe is a slot of the positioning
subframe.
18. The wireless communications apparatus of claim 17, wherein the
slot of the positioning subframe is adjacent to a disparate slot of
the positioning subframe that includes a set of resource elements
reserved for transmitting control data.
19. The wireless communications apparatus of claim 17, wherein the
one or more resource elements are in consecutive orthogonal
frequency division multiplexing (OFDM) symbols in the slot of the
positioning subframe.
20. The wireless communications apparatus of claim 19, wherein the
one or more resource elements include shifted subcarriers of the
consecutive OFDM symbols.
21. The wireless communications apparatus of claim 20, wherein the
shifted subcarriers correspond to a diagonal pattern.
22. The wireless communications apparatus of claim 16, wherein the
at least one processor determines the one or more resource elements
according to a planned selection function or a pseudo-random
selection function.
23. The wireless communications apparatus of claim 16, wherein the
at least one processor is further configured to apply a transmit
diversity scheme to the PRS.
24. An apparatus, comprising: means for determining a positioning
subframe configured for transmitting positioning reference signals
(PRS); means for selecting one or more resource elements in the
positioning subframe, excluding a set of resource elements
allocated for transmitting cell-specific reference signals (CRS),
for transmitting a PRS; and means for transmitting the PRS in the
one or more resource elements.
25. The apparatus of claim 24, wherein the means for determining
the positioning subframe determines at least a portion of a slot of
the positioning subframe configured for transmitting PRSs.
26. The apparatus of claim 25, wherein the at least the portion of
the slot is adjacent to a disparate slot of the positioning
subframe that includes a disparate portion allocated for
transmitting control data.
27. The apparatus of claim 25, wherein the means for selecting one
or more resource elements in the positioning subframe selects the
one or more resource elements from consecutive orthogonal frequency
division multiplexing (OFDM) symbols in the slot of the positioning
subframe.
28. The apparatus of claim 27, wherein the means for selecting one
or more resource elements in the positioning subframe selects the
one or more resource elements as shifted subcarriers in each of the
consecutive OFDM symbols.
29. The apparatus of claim 28, wherein the one or more resource
elements form a diagonal pattern.
30. The apparatus of claim 24, further comprising means for
applying a transmit diversity scheme to the PRS.
31. A computer program product, comprising: a computer-readable
medium comprising: code for causing at least one computer to select
a portion of a positioning subframe for transmitting positioning
reference signals (PRS); code for causing the at least one computer
to determine one or more resource elements in the positioning
subframe, excluding a plurality of disparate resource elements
allocated for transmitting cell-specific reference signals (CRS),
for transmitting a PRS; and code for causing the at least one
computer to transmit the PRS in the one or more resource
elements.
32. The computer program product of claim 31, wherein the portion
of the positioning subframe is a slot of the positioning
subframe.
33. The computer program product of claim 32, wherein the slot of
the positioning subframe is adjacent to a disparate slot of the
positioning subframe that includes a set of resource elements
reserved for transmitting control data.
34. The computer program product of claim 32, wherein the one or
more resource elements are comprise within consecutive orthogonal
frequency division multiplexing (OFDM) symbols in the slot of the
positioning subframe.
35. The computer program product of claim 34, wherein the one or
more resource elements are comprised within subcarriers shifted
among the consecutive OFDM symbols according to a pattern.
36. The computer program product of claim 35, wherein the pattern
is a diagonal pattern.
37. An apparatus, comprising: a special slot selecting component
that determines a positioning subframe configured for transmitting
positioning reference signals (PRS); a PRS resource element
selecting component that selects one or more resource elements in
the positioning subframe, excluding a set of resource elements
allocated for transmitting cell-specific reference signals (CRS),
for transmitting a PRS; and a PRS transmitting component that
transmits the PRS in the one or more resource elements.
38. The apparatus of claim 37, wherein the special slot selecting
component determines at least a portion of a slot of the
positioning subframe configured for transmitting PRSs.
39. The apparatus of claim 38, wherein the at least the portion of
the slot is adjacent to a disparate slot of the positioning
subframe that includes a disparate portion allocated for
transmitting control data.
40. The apparatus of claim 39, wherein the PRS resource element
selecting component selects the one or more resource elements from
consecutive orthogonal frequency division multiplexing (OFDM)
symbols in the slot of the positioning subframe.
41. The apparatus of claim 40, wherein the PRS resource element
selecting component selects the one or more resource elements as
shifted subcarriers in each of the consecutive OFDM symbols.
42. The apparatus of claim 41, wherein the one or more resource
elements form a diagonal pattern.
43. A method, comprising: selecting one or more subframes as one or
more positioning subframes for blanking data transmissions; and
indicating one or more of the one or more positioning subframes as
one or more multicast/broadcast single frequency network (MBSFN)
subframes to additionally blank cell-specific reference signal
(CRS) transmission over the one or more MBSFN subframes.
44. The method of claim 43, further comprising determining the one
or more positioning subframes as the one or more MBSFN subframes
according to a planned pattern or a pseudo-random pattern.
45. The method of claim 44, wherein the planned pattern or the
pseudo-random pattern is received from a network specification,
configuration, or hardcoding.
46. The method of claim 43, further comprising transmitting a
CRS-like waveform in at least one of the one or more MBSFN
subframes.
47. A wireless communications apparatus, comprising: at least one
processor configured to: determine one or more subframes as one or
more positioning subframes for blanking data transmissions; discern
one or more of the one or more positioning subframes as one or more
multicast/broadcast single frequency network (MBSFN) subframes to
additionally blank cell-specific reference signal (CRS)
transmission over the one or more MBSFN subframes; and indicate the
one or more MBSFN subframes as MBSFN subframes; and a memory
coupled to the at least one processor.
48. An apparatus, comprising: means for selecting one or more
subframes as one or more positioning subframes for blanking data
transmissions; means for determining the one or more positioning
subframes as one or more multicast/broadcast single frequency
network (MBSFN) subframes; and means for indicating the one or more
MBSFN subframes as MBSFN subframes.
49. A computer program product, comprising: a computer-readable
medium comprising: code for causing at least one computer to select
one or more subframes as one or more positioning subframes for
blanking data transmissions; and code for causing the at least one
computer to indicate the one or more positioning subframes as one
or more multicast/broadcast single frequency network (MBSFN)
subframes to additionally blank cell-specific reference signal
(CRS) transmission over the one or more MBSFN subframes.
50. An apparatus, comprising: a positioning subframe selecting
component that determines one or more subframes as one or more
positioning subframes for blanking data transmissions; a
multicast/broadcast single frequency network (MBSFN) subframe
determining component that selects the one or more positioning
subframes as one or more MBSFN subframes; and an MBSFN subframe
specifying component that indicates the one or more MBSFN subframes
as MBSFN subframes.
Description
CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/142,784, filed Jan. 6, 2009, and entitled
"A METHOD AND APPARATUS FOR IMPROVING HEARABILITY FOR DISCONTINUOUS
PILOT SYSTEM," U.S. Provisional Application Ser. No. 61/144,075,
filed Jan. 12, 2009, and entitled "A METHOD AND APPARATUS FOR
IMPROVING HEARABILITY FOR DISCONTINUOUS PILOT SYSTEM," U.S.
Provisional Application Ser. No. 61/149,647, filed Feb. 3, 2009,
and entitled "A METHOD AND APPARATUS FOR IMPROVING HEARABILITY FOR
DISCONTINUOUS PILOT SYSTEM," U.S. Provisional Application Ser. No.
61/151,128, filed Feb. 9, 2009, and entitled "A METHOD AND
APPARATUS FOR IMPROVING HEARABILITY FOR DISCONTINUOUS PILOT
SYSTEM," U.S. Provisional Application Ser. No. 61/163,429, filed
Mar. 25, 2009, and entitled "A METHOD AND APPARATUS FOR IMPROVING
HEARABILITY FOR DISCONTINUOUS PILOT SYSTEM," the entireties of
which are incorporated herein by reference.
BACKGROUND
[0002] I. Field
[0003] The present disclosure relates generally to wireless
communications and more specifically to transmitting reference
signals to improve hearability thereof.
[0004] II. Background
[0005] Wireless communication systems are widely deployed to
provide various types of communication content such as, for
example, voice, data, and so on. Typical wireless communication
systems may be multiple-access systems capable of supporting
communication with multiple users by sharing available system
resources (e.g., bandwidth, transmit power, . . . ). Examples of
such multiple-access systems may include code division multiple
access (CDMA) systems, time division multiple access (TDMA)
systems, frequency division multiple access (FDMA) systems,
orthogonal frequency division multiple access (OFDMA) systems, and
the like. Additionally, the systems can conform to specifications
such as third generation partnership project (3GPP), 3GPP long term
evolution (LTE), ultra mobile broadband (UMB), etc.
[0006] Generally, wireless multiple-access communication systems
may simultaneously support communication for multiple mobile
devices. Each mobile device may communicate with one or more access
points (e.g., base stations, femtocells, picocells, relay nodes,
and/or the like) via transmissions on forward and reverse links.
The forward link (or downlink) refers to the communication link
from access points to mobile devices, and the reverse link (or
uplink) refers to the communication link from mobile devices to
access points. Further, communications between mobile devices and
access points may be established via single-input single-output
(SISO) systems, multiple-input single-output (MISO) systems,
multiple-input multiple-output (MIMO) systems, and so forth. In
addition, mobile devices can communicate with other mobile devices
(and/or access points with other access points) in peer-to-peer
wireless network configurations.
[0007] Access points in wireless networks can transmit
cell-specific reference signals (CRS) to facilitate identifying
cells of the access points; in addition, the CRSs can be utilized
to determine a location of one or more mobile devices or other
devices using trilateration or similar location mechanisms. For
example, techniques such as observed time difference of arrival
(OTDOA) in universal mobile telecommunication system (UMTS) are
used to compute a possible location of a device based at least in
part on measuring a time difference of multiple signals received
and/or location of the transmitter of each signal. Similar
techniques in other technologies include enhanced observed time
difference (E-OTD) in global system for mobile communications (GSM)
enhanced data rates for GSM evolution (EDGE) radio access network
(GERAN), advanced forward link trilateration (AFLT) in CDMA2000,
etc.
[0008] In addition, technologies such as idle period down link
(IPDL) and time-aligned IDPL (TA-IPDL) in UMTS, as well as highly
detectable pilot (HDP) in CDMA2000, improve hearability of the CRSs
by blanking (e.g., temporarily ceasing) transmissions over certain
periods of time. In IPDL, one or more access points can blank
transmission in a different period of time (e.g., a slot of
subframe defined as an IPDL period) allowing a device to measure
CRSs of access points that are normally strongly interfered by
other access points during the periods where the interfering access
points blank transmissions. Performance gains, however, are limited
by blanking only one interfering access point in a given IPDL
period. In TA-IPDL, the access points can define a similar common
time period, referred to as a TA-IPDL period. During this period,
some access points will blank transmissions while others transmit
an access-point specific pilot allowing devices to measure this
pilot free from substantial interference. The HDP concept in
CDMA2000 uses the same principle as TA-IPDL. TA-IPDL, however, is
not always applicable in asynchronous networks. Moreover, in IPDL
and TA-IPDL, legacy mobiles that are not aware of the periods of
time for blanking and/or transmitting common pilots, can cause data
errors. For example, lack of pilots or pilot modification can
result in channel estimation errors and/or hybrid automatic
repeat/request (HARD) buffers corruption due to the assumption that
the pilots exist.
SUMMARY
[0009] The following presents a simplified summary of various
aspects of the claimed subject matter in order to provide a basic
understanding of such aspects. This summary is not an extensive
overview of all contemplated aspects, and is intended to neither
identify key or critical elements nor delineate the scope of such
aspects. Its sole purpose is to present some concepts of the
disclosed aspects in a simplified form as a prelude to the more
detailed description that is presented later.
[0010] In accordance with one or more embodiments and corresponding
disclosure thereof, various aspects are described in connection
with facilitating defining a set of time periods for transmitting
positioning reference signals at various access points. In
particular, an access point can transmit cell-specific reference
signals (CRS) in a portion of a time period defined for
transmitting such CRSs while other access points blank transmission
over the time period. During a disparate portion of the time period
reserved for transmitting CRSs, one or more access points can
transmit positioning reference signals (PRS). In one example, the
PRSs can be transmitted by access points in planned or
pseudo-randomly selected time-frequency regions, for example single
or group (consecutive or otherwise) of subframes, slots, resource
blocks, subbands, etc., to increase hearability thereof. In
addition, PRSs can be transmitted by the access points according to
one or more transmit diversity schemes to mitigate interference
among the PRSs. In one example, a remaining portion of the time
period allocated for transmitting CRSs, which would otherwise
remain blanked by other access points, is leveraged for PRS
transmission allowing devices to receive the PRSs without
substantial interference. It is to be appreciated, in one example,
that the PRS can be utilized for trilateration to determine a
location of a receiving device.
[0011] According to related aspects, a method is provided that
includes determining a positioning subframe configured for
transmitting PRSs and selecting one or more resource elements in
the positioning subframe for transmitting a PRS avoiding resource
elements in the positioning subframe configured for transmitting a
CRS. The method also includes transmitting the PRS in the one or
more resource elements.
[0012] Another aspect relates to a wireless communications
apparatus. The wireless communications apparatus can include at
least one processor configured to select a portion of a positioning
subframe for transmitting PRSs and determine one or more resource
elements in the positioning subframe, excluding a plurality of
disparate resource elements allocated for transmitting CRSs, for
transmitting a PRS. The at least one processor is further
configured to transmit the PRS in the one or more resource
elements. The wireless communications apparatus also comprises a
memory coupled to the at least one processor.
[0013] Yet another aspect relates to an apparatus. The apparatus
includes means for determining a positioning subframe configured
for transmitting PRSs and means for selecting one or more resource
elements in the positioning subframe, excluding a set of resource
elements allocated for transmitting CRSs, for transmitting a PRS.
The apparatus further includes means for transmitting the PRS in
the one or more resource elements.
[0014] Still another aspect relates to a computer program product,
which can have a computer-readable medium including code for
causing at least one computer to select a portion of a positioning
subframe for transmitting PRSs and code for causing the at least
one computer to determine one or more resource elements in the
positioning subframe, excluding a plurality of disparate resource
elements allocated for transmitting CRSs, for transmitting a PRS.
The computer-readable medium can also comprise code for causing the
at least one computer to transmit the PRS in the one or more
resource elements.
[0015] Moreover, an additional aspect relates to an apparatus that
includes a special slot selecting component that determines a
positioning subframe configured for transmitting PRSs and a PRS
resource element selecting component that selects one or more
resource elements in the positioning subframe, excluding a set of
resource elements allocated for transmitting CRSs, for transmitting
a PRS. The apparatus can further include a PRS transmitting
component that transmits the PRS in the one or more resource
elements.
[0016] According to another aspect, a method is provided that
includes selecting one or more subframes as one or more positioning
subframes for blanking data transmissions and indicating one or
more of the one or more positioning subframes as one or more
multicast/broadcast single frequency network (MBSFN) subframes to
additionally blank CRS transmission over the one or more MBSFN
subframes
[0017] Another aspect relates to a wireless communications
apparatus. The wireless communications apparatus can include at
least one processor configured to determine one or more subframes
as one or more positioning subframes for blanking data
transmissions. The at least one processor is further configured to
discern one or more of the one or more positioning subframes as one
or more MBSFN subframes to additionally blank CRS transmission over
the one or more MBSFN subframes and indicate the one or more MBSFN
subframes as MBSFN subframes. The wireless communications apparatus
also comprises a memory coupled to the at least one processor.
[0018] Yet another aspect relates to an apparatus. The apparatus
includes means for selecting one or more subframes as one or more
positioning subframes for blanking data transmissions and means for
determining the one or more positioning subframes as one or more
MBSFN subframes. The apparatus further includes means for
indicating the one or more MBSFN subframes as MBSFN subframes.
[0019] Still another aspect relates to a computer program product,
which can have a computer-readable medium including code for
causing at least one computer to select one or more subframes as
one or more positioning subframes for blanking data transmissions.
The computer-readable medium can also comprise code for causing the
at least one computer to indicate the one or more positioning
subframes as one or more MBSFN subframes to additionally blank CRS
transmission over the one or more MBSFN subframes.
[0020] Moreover, an additional aspect relates to an apparatus that
includes a positioning subframe selecting component that determines
one or more subframes as one or more positioning subframes for
blanking data transmissions and a MBSFN subframe determining
component that selects the one or more positioning subframes as one
or more MBSFN subframes. The apparatus can further include an MBSFN
subframe specifying component that indicates the one or more MBSFN
subframes as MBSFN subframes.
[0021] To the accomplishment of the foregoing and related ends, the
one or more embodiments comprise the features hereinafter fully
described and particularly pointed out in the claims. The following
description and the annexed drawings set forth in detail certain
illustrative aspects of the one or more embodiments. These aspects
are indicative, however, of but a few of the various ways in which
the principles of various embodiments may be employed, and the
described embodiments are intended to include all such aspects and
their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a block diagram of a system for transmitting
cell-specific reference signals (CRS) and positioning reference
signals (PRS).
[0023] FIG. 2 is an illustration of an example communications
apparatus for employment within a wireless communications
environment.
[0024] FIG. 3 illustrates an example positioning subframe with
resource elements allocated for CRS and PRS transmission.
[0025] FIG. 4 illustrates example positioning subframes with
control regions and resource elements allocated for CRS and PRS
transmission.
[0026] FIG. 5 illustrates an example positioning
multicast/broadcast single frequency network (MBSFN) subframe.
[0027] FIG. 6 illustrates example subband allocations to promote
hearability of PRS transmissions.
[0028] FIG. 7 is an illustration of an example communications
apparatus for employment within a wireless communications
environment.
[0029] FIG. 8 is a flow diagram of an example methodology that
transmits PRSs in positioning subframes improving hearability
thereof.
[0030] FIG. 9 is a flow diagram of an example methodology that
transmits PRSs in positioning subframes indicated as MBSFN
subframes.
[0031] FIG. 10 is a flow diagram of an example methodology that
indicates positioning subframes as MBSFN subframes to control CRS
transmission thereover.
[0032] FIG. 11 is a flow diagram of an example methodology that
indicates positioning subframes as MBSFN subframes and transmits
CRS-like waveforms thereover.
[0033] FIG. 12 is a block diagram of an example apparatus that
facilitates transmitting PRSs in positioning subframes.
[0034] FIG. 13 is a block diagram of an example apparatus that
facilitates indicating positioning subframes as MBSFN subframes to
control transmitting CRSs.
[0035] FIGS. 14-15 are block diagrams of example wireless
communication devices that can be utilized to implement various
aspects of the functionality described herein.
[0036] FIG. 16 illustrates an example wireless multiple-access
communication system in accordance with various aspects set forth
herein.
[0037] FIG. 17 is a block diagram illustrating an example wireless
communication system in which various aspects described herein can
function.
DETAILED DESCRIPTION
[0038] Various aspects of the claimed subject matter are now
described with reference to the drawings, wherein like reference
numerals are used to refer to like elements throughout. In the
following description, for purposes of explanation, numerous
specific details are set forth in order to provide a thorough
understanding of one or more aspects. It may be evident, however,
that such aspect(s) may be practiced without these specific
details. In other instances, well-known structures and devices are
shown in block diagram form in order to facilitate describing one
or more aspects.
[0039] As used in this application, the terms "component,"
"module," "system," and the like are intended to refer to a
computer-related entity, either hardware, firmware, a combination
of hardware and software, software, or software in execution. For
example, a component can be, but is not limited to being, a process
running on a processor, an integrated circuit, an object, an
executable, a thread of execution, a program, and/or a computer. By
way of illustration, both an application running on a computing
device and the computing device can be a component. One or more
components can reside within a process and/or thread of execution
and a component can be localized on one computer and/or distributed
between two or more computers. In addition, these components can
execute from various computer readable media having various data
structures stored thereon. The components can communicate by way of
local and/or remote processes such as in accordance with a signal
having one or more data packets (e.g., data from one component
interacting with another component in a local system, distributed
system, and/or across a network such as the Internet with other
systems by way of the signal).
[0040] Furthermore, various aspects are described herein in
connection with a wireless terminal and/or a base station. A
wireless terminal can refer to a device providing voice and/or data
connectivity to a user. A wireless terminal can be connected to a
computing device such as a laptop computer or desktop computer, or
it can be a self contained device such as a personal digital
assistant (PDA). A wireless terminal can also be called a system, a
subscriber unit, a subscriber station, mobile station, mobile,
remote station, access point, remote terminal, access terminal,
user terminal, user agent, user device, or user equipment (UE). A
wireless terminal can be a subscriber station, wireless device,
cellular telephone, PCS telephone, cordless telephone, a Session
Initiation Protocol (SIP) phone, a wireless local loop (WLL)
station, a personal digital assistant (PDA), a handheld device
having wireless connection capability, or other processing device
connected to a wireless modem. A base station (e.g., access point
or Evolved Node B (eNB)) can refer to a device in an access network
that communicates over the air-interface, through one or more
sectors, with wireless terminals. The base station can act as a
router between the wireless terminal and the rest of the access
network, which can include an Internet Protocol (IP) network, by
converting received air-interface frames to IP packets. The base
station also coordinates management of attributes for the air
interface.
[0041] Moreover, various functions described herein can be
implemented in hardware, software, firmware, or any combination
thereof. If implemented in software, the functions can be stored on
or transmitted over as one or more instructions or code on a
computer-readable medium. Computer-readable media includes both
computer storage media and communication media including any medium
that facilitates transfer of a computer program from one place to
another. A storage media can be any available media that can be
accessed by a computer. By way of example, and not limitation, such
computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or
other optical disk storage, magnetic disk storage or other magnetic
storage devices, or any other medium that can be used to carry or
store desired program code in the form of instructions or data
structures and that can be accessed by a computer. Also, any
connection is properly termed a computer-readable medium. For
example, if the software is transmitted from a website, server, or
other remote source using a coaxial cable, fiber optic cable,
twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared, radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave are included in
the definition of medium. Disk and disc, as used herein, includes
compact disc (CD), laser disc, optical disc, digital versatile disc
(DVD), floppy disk and blu-ray disc (BD), where disks usually
reproduce data magnetically and discs reproduce data optically with
lasers. Combinations of the above should also be included within
the scope of computer-readable media.
[0042] Various techniques described herein can be used for various
wireless communication systems, such as Code Division Multiple
Access (CDMA) systems, Time Division Multiple Access (TDMA)
systems, Frequency Division Multiple Access (FDMA) systems,
Orthogonal Frequency Division Multiple Access (OFDMA) systems,
Single Carrier FDMA (SC-FDMA) systems, and other such systems. The
terms "system" and "network" are often used herein interchangeably.
A CDMA system can implement a radio technology such as Universal
Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes
Wideband-CDMA (W-CDMA) and other variants of CDMA. Additionally,
CDMA2000 covers the IS-2000, IS-95 and IS-856 standards. A TDMA
system can implement a radio technology such as Global System for
Mobile Communications (GSM). An OFDMA system can implement a radio
technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband
(UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,
Flash-OFDM.RTM., etc. UTRA and E-UTRA are part of Universal Mobile
Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) is
an upcoming release that uses E-UTRA, which employs OFDMA on the
downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE and GSM
are described in documents from an organization named "3rd
Generation Partnership Project" (3GPP). Further, CDMA2000 and UMB
are described in documents from an organization named "3rd
Generation Partnership Project 2" (3GPP2).
[0043] Various aspects will be presented in terms of systems that
can include a number of devices, components, modules, and the like.
It is to be understood and appreciated that the various systems can
include additional devices, components, modules, etc. and/or can
not include all of the devices, components, modules etc. discussed
in connection with the figures. A combination of these approaches
can also be used.
[0044] Referring now to the drawings, FIG. 1 illustrates an example
wireless network 100 that facilitates transmitting cell-specific
reference signals (CRS) and positioning reference signals (PRS).
Wireless network 100 includes an access point 102 that can provide
wireless network access to one or more devices. Access point 102,
for example, can be an access point, such as a macrocell access
point, femtocell or picocell access point, eNB, mobile base
station, a portion thereof, and/or substantially any device that
provides access to a wireless network. In addition, wireless
network 100 includes a wireless device 104 that receives access to
a wireless network. Wireless device 104, for example, can be a
mobile device, such as a UE, a portion thereof, and/or
substantially any device that receives access to a wireless
network. It is to be appreciated that the components shown and
described in access point 102 can be present in wireless device 104
and/or vice versa, in one example, to facilitate functionality
described below.
[0045] Access point 102 can include a CRS scheduling component 106
that determines one or more time periods for scheduling CRS
transmission, a PRS scheduling component 108 that selects one or
more time periods for transmitting PRSs, a silencing component 110
that discerns one or more time periods during which to cease data
transmissions, and a transmitting component 112 that transmits the
CRS and/or PRS and ceases transmissions over the silent time
periods. Wireless device 104 comprises a CRS receiving component
114 that obtains one or more CRSs of one or more access points
during certain time periods and a PRS receiving component 116 that
determines one or more PRSs received during a portion of the
certain time periods during which the one or more CRSs are
received.
[0046] According to an example, CRS scheduling component 106 can
select a portion of a time period for transmitting CRSs. This can
be defined according to a standard, a network specification,
configuration, hardcoding, a received variable, and/or the like,
for example. The CRS scheduling component 106, in one example, can
select a similar portion of a number of time periods for
transmitting the CRS, such as one or more portions of a subframe or
multiple subframes, which can be consecutive or otherwise.
Transmitting component 112 can transmit the CRS in the portion of
the time period. In addition, PRS scheduling component 108 can
select a disparate portion of one or more of the time periods for
additionally transmitting PRSs, such as one or more subframes. In
an example, PRS scheduling component 108 can select the one or more
time periods according to a pseudo-random or planned selection
function, which can be based on a standard, network specification,
configuration, hardcoding, etc. Moreover, for example, the one or
more time periods can be substantially aligned among one or more
access points.
[0047] Similarly, PRS scheduling component 108 can select the
disparate portion of the one or more of the time periods according
to a standard, a network specification, configuration, hardcoding,
etc., pseudo-randomly according to such, using one or more
sequences, such as pseudo-random binary sequences followed by
quadrature amplitude modulation (QAM) (e.g., quadrature phase-shift
keying (QPSK)), or sequences that ease detectability such as
Zadoff-Chu sequences, Walsh sequences, and/or the like, using
sequences formed by encoding a payload (e.g., using a low reuse
preamble), etc. In addition, transmitting component 112 can
transmit the PRSs using one or more disparate transmit diversity
schemes, such as precoding vector switching (PVS), small cyclic
delay diversity (CDD), etc. to minimize receiver impact due to
introducing the one or more time periods and PRSs. Moreover, in
this regard, transmitting component 112 can transmit the PRSs (and
CRSs) over a single antenna port (or a single virtual antenna over
multiple physical antennas) using the one or more transmit
diversity schemes.
[0048] In addition, transmitting component 112 can transmit the PRS
over the disparate portion of the one or more time periods.
Silencing component 110 can cease transmission by access point 102
over the remaining portions of the one or more time periods
selected by the PRS scheduling component 108. CRS receiving
component 114 can obtain the CRS transmitted by access point 102
for identifying the access point, for example, as well as the PRS
for utilization in trilateration location for wireless device 104.
In this example, by transmitting PRSs in available portions of the
one or more time periods, hearability is improved for wireless
devices as other interfering access points can be silent while the
PRS for a disparate access point is transmitted, but can still
transmit CRSs. This can also ensure correct channel estimation for
legacy device support.
[0049] According to one example, wireless network 100 can be an LTE
network such that access point 102 and wireless device 104
communicate according to an LTE standard. An LTE system can be an
orthogonal frequency division multiplexing (OFDM) system in which
data is communicated in 1 millisecond (ms) subframes. A subframe
can be defined as a portion of frequency over time (e.g., 1 ms).
For example, the subframe can include a number of contiguous or
non-contiguous OFDM symbols, which are portions of frequency over
time and can be divided into smaller resource elements
representative of a number of frequency carriers over the OFDM
symbols. Consecutive resource elements over the OFDM symbols can be
referred to as a resource block, for example. In addition, each
subframe can have two slots, for example, that are thus also
defined by a number of OFDM symbols and/or resource elements
thereof, where control data is transmitted over a portion of a
first slot (over one or more OFDM symbols) and user plane data is
transmitted over the remainder of the first slot and the entire
second slot.
[0050] In this example, CRS scheduling component 106, according to
the LTE specification, can schedule a plurality of CRSs (e.g., 2
CRSs) for transmission in each slot, transmitted over a plurality
of resource elements. CRS receiving component 114, for example, can
obtain the CRSs for data demodulation purposes, for cell specific
measurements in cell selection/reselection and handover, etc. In
addition, however, PRS scheduling component 108 can select special
slots, which can be certain time-frequency regions, for
transmitting PRSs. As described, this can be according to an LTE
specification, which can use an idle period down link (IPDL),
time-aligned IDPL (TA-IPDL), highly detectable pilot (HDP), or
similar scheme to define the special slots. In this regard, the
special slots can be different for each access point (e.g.,
selected according to a pseudo-random scheme), similar
substantially time-aligned special slots across access points,
and/or the like. Moreover, the special slot can be the second slot
of the respective subframes (e.g., in an LTE configuration) so as
not to interfere with control data transmissions in the first slot,
and/or a portion of the first slot of the respective subframes that
are not utilized for transmitting control data.
[0051] The PRS scheduling component 108 can select one or more
resource elements as the frequency region for special slots, over
which CRSs are not transmitted, for transmitting a PRS related to
access point 102. Though not shown, other access points can also
select one or more resource elements for transmitting PRSs. In this
regard, PRS scheduling component 108, in one example, can schedule
PRSs according to one or more sequences that ease detectability
and/or mitigate interference, such as Zadoff-Chu sequences, Walsh
sequences, QPSK sequences, etc., as described. Additionally, as
shown above, transmitting component 112 can transmit the PRS in the
resource elements of the special slots, and can do so using
transmit diversity, such as PVS, CDD, etc., in one example. PRS
receiving component 116 can obtain the PRS for the access point
102, and wireless device 104 can perform trilateration, or another
positioning algorithm, in one example. Moreover, for example, in
the special slots for transmitting PRSs where PRSs for access point
102 are not received, PRS receiving component 116 can receive PRSs
for one or more disparate access points, for example. These PRSs
can additionally or alternatively be used in trilateration,
etc.
[0052] In addition, silencing component 110 can ensure that
transmission is ceased for remaining resource elements in the
special slots; thus, access point 102 does not transmit data in the
special slots or any signals other than the aforementioned CRS(s)
(which can be mandatory) and PRS(s) (which can be optional, on a
pseudorandom basis). It is to be appreciated, however, that a
portion of the special slots, as opposed to the entire slot, can be
utilized for transmitting PRSs, within which silencing component
110 ensures transmission is ceased for remaining portion of the
special slot and not necessarily the entire remaining slot.
[0053] Referring next to FIG. 2, a communications apparatus 200
that can participate in a wireless communications network is
illustrated. The communications apparatus 200 can be an access
point, a mobile device, a portion thereof, or substantially any
device that receives communications in a wireless network. The
communications apparatus 200 can include a special slot selecting
component 202 that determines one or more slots or subframes (or
other time/frequency regions) for transmitting one or more PRSs,
which can be referred to as positioning subframes when the special
slot comprises one subframe, a PRS resource element selecting
component 204 that discerns one or more resource elements within
the special slot for transmitting the one or more PRSs, a PRS
transmit diversity component 206 that applies a transmit diversity
scheme to the one or more PRSs to facilitate differentiating PRSs
of various communications apparatuses, a PRS transmitting component
208 that can communicate a PRS in a selected slot over a selected
resource element using an optional transmit diversity, and a data
scheduling component 210 that can select resources for
communicating user plane data in a wireless network.
[0054] According to an example, special slot selecting component
202 can determine one or more special slots and/or related
subframes for transmitting PRSs (e.g., and blanking data
transmissions). In one example, the special slots or positioning
subframes can be defined in a network specification or standard,
and special slot selecting component 202 selects the special slots
or positioning subframes based on a standard, network
specification, hardcoding, configuration, and/or similar
information. Additionally or alternatively, special slot selecting
component 202 can select the slots as one or more slots reserved
for IPDL, TA-IPDL, HDP, or similar slot.
[0055] For example, IPDL can be used in asynchronous networks such
that IPDL slots (e.g., slots that are blanked at a respective
communications apparatus) are selected pseudo-randomly or according
to some pattern to facilitate diversity in blanking the IPDL slots.
In another example, TA-IPDL or HDP can be utilized in synchronous
networks such that TA-IPDL or HDP slots are substantially aligned
at communications apparatuses. As described previously, in TA-IPDL
or HDP, some communications apparatuses in a set transmit pilots in
the TA-IPDL slots while the remaining communications apparatuses in
the set blank transmission in the slots. Determining which
communications apparatuses transmit and which blank can
additionally be assigned pseudo-randomly or according to a planned
deployment based on a standard, network specification, hardcoding,
configuration, etc., which can be based on an identifier of the
communications apparatus, and/or the like, in one example.
[0056] In another example, special slot selecting component 202 can
determine the one or more slots based at least in part on a
standard, network specification, hardcoding, configuration, a
received communication from a wireless network or related device,
and/or the like. For example, special slot selecting component 202
can receive slot information from one or more communications
apparatuses (e.g., over a backhaul link), detect a CRS transmission
from one or more communications apparatuses and select the slot
over which the CRS is detected for transmitting PRSs, and/or the
like. Moreover, as described, special slot selecting component 202
can, in one example, select a second slot of respective positioning
subframes for transmitting PRSs. Additionally or alternatively,
special slot selecting component 202 can select a portion of the
first slot that excludes a control channel portion for transmitting
PRSs. Moreover, special slot selecting component 202 can select a
portion of a slot for transmitting PRSs. Additionally, special slot
selecting component 202 can select a set of consecutive positioning
subframes for transmitting PRSs.
[0057] Similarly, PRS resource element selecting component 204 can
determine one or more resource elements within the one or more
special slots for transmitting the PRS. PRS resource element
selecting component 204 can select the resource elements according
to a PRS pattern, as described in further detail below. As
described, PRS resource element selecting component 204 can
determine the resource elements according to a pseudo-random
selection function (e.g., based on a cell identifier of a cell of
the communications apparatus 200) and/or according to a planned
selection function. In any case, PRS resource element selecting
component 204, in one example, can retrieve the selection function
for determining the PRS pattern based on a standard, network
specification, hardcoding, configuration, and/or the like. By
selecting slots that are silent with respect to data transmissions
and CRSs and using remaining resources of the slots with a reuse
scheme, hearability of the PRSs is improved over the otherwise
silent resource elements in the subframe.
[0058] Once one or more special slots and related resource elements
are selected, PRS transmit diversity component 206 can optionally
apply a transmission diversity scheme to the PRS. For example, PVS,
small CDD, and/or the like can be applied to PRSs to minimize
standards and receiver impact caused by introduction of the PRSs
and positioning subframes or slots. In another example,
non-transparent diversity schemes can be utilized as well. For
instance, this allows the PRS transmitting component 208 to
transmit PRSs over a single antenna port (or a single virtual
antenna port over multiple physical antennas). In either case, for
example, PRS transmit diversity component 206 can additionally
signal necessary information (e.g., delay between different
transmit antennas in CDD) to a receiving device. In another
example, PRS transmit diversity component 206 can apply a diversity
scheme that utilizes different sets of tones for transmitting
disparate PRSs. Thus, for example, a set of tones can be selected
by PRS transmit diversity component 206 for transmitting a first
PRS, and PRS transmit diversity component 206 can select a
disparate set of tones for transmitting a subsequent PRS.
[0059] In any case, PRS transmitting component 208 can transmit the
PRSs in the selected resource elements of the selected slot(s) (or
portion thereof) according to one or more transmit diversity
schemes (if present). In addition, PRS transmitting component 208
can boost energy of the PRSs or reshape its spectrum since
communications apparatus 200 does not transmit other data in the
selected slot(s) (or portion thereof). In addition, data scheduling
component 210 can select one or more resources for transmitting
user plane data of communications apparatus 200. In this example,
data scheduling component 210 can avoid scheduling data over the
slot(s) (or portion thereof) selected for transmitting PRSs so as
not to interfere with the PRSs. This allows receiving devices to
receive and measure PRSs without significant interference from
surrounding communications apparatuses, as described.
[0060] In another example, to introduce functionality described
herein in a backward compatible manner, PRS transmitting component
208 can indicate the selected slots or related subframes as
allocated for multicast/broadcast single frequency network (MBSFN)
signals. In this regard, previous versions of wireless devices
(e.g., an LTE release-8 UE) can avoid non-control regions of the
MBSFN subframes. Thus, such legacy devices will not attempt to
process the CRSs given that they are not transmitted in the
non-control region of MBSFN subframes. For example, the MBSFN
subframes can be designated as positioning subframes for
transmitting PRSs and can have a higher value periodicity (e.g.,
80/160/320 ms). Moreover, the physical control region and cyclic
prefix (CP) of the control and non-control regions can be the same
as in an MBSFN subframe of mixed carrier to facilitate indicating
the subframe as MBSFN and detection as an MBSFN subframe by a
legacy device. Other wireless devices, however, can be aware of the
use of MBSFN indicated subframes for transmitting the PRSs and can
accordingly utilize the PRSs, as described.
[0061] Now referring to FIG. 3, illustrated is an example
positioning subframe 300 in a wireless network. For example,
positioning subframe 300 can be an OFDM subframe, as described.
Positioning subframe 300 can be a subframe (e.g., a 1 ms or similar
subframe) in an LTE system communicated by an access point to one
or more wireless devices. For example, access points in a wireless
network (not shown) can blank user plane data transmissions over
positioning subframe 300, as described herein.
[0062] Positioning subframe 300 comprises two slots 302 and 304,
each comprising a number of resource elements. As described, in a
first slot of a given subframe in LTE, control data can be
transmitted over a portion of the resource elements (e.g., over one
or more initial OFDM symbols). In this regard, CRSs can be
transmitted by various access points in resource element 306, and
similarly patterned resource elements, in the first slot 302, along
with optionally control data (not shown). User plane data
transmissions by a given access point can be ceased over the
remaining resource elements of the slot to allow receipt of the
CRSs without substantial interference from other transmissions.
[0063] In slot 304, PRSs can be transmitted by various access
points at resource element 308, and similarly patterned resource
elements in slot 304. In this regard, slot 304 can be the special
slot selected for transmitting PRSs. Moreover, thus, the PRSs do
not interfere with control data transmissions. In addition, by
transmitting PRSs in the resource elements that are otherwise
silenced by the access points, hearability of the PRSs is improved.
As described, PRS resource element 308, and similarly patterned
resource elements in slot 304, can be collectively defined as a PRS
pattern. The PRS pattern can be a diagonal pattern, as depicted,
assigned by the access points for transmitting PRSs. In this
regard, for example, an access point can utilize different
subcarriers in different OFDM symbols for transmitting PRSs, aside
from those utilized for transmitting CRSs in the depicted example.
In an example, using substantially all subcarriers in the resource
block (or slot 304) over the duration of slot 304. This ensures a
channel estimation provided by the PRS is of maximum possible
length and mitigates ambiguity with respect to cyclic shifts. In an
example, using the different subcarriers in OFDM symbols that form
a diagonal pattern is one way of utilizing the substantially all
subcarriers in the resource block.
[0064] According to an example, the PRS patterns can be assigned
according to a standard or network specification, which can be
hardcoded in the access point implementation, a configuration, etc.
In addition, other than being diagonal patterns, the PRS patterns
can employ substantially configuration such that there is a PRS
transmitted in each OFDM symbol of a special slot and/or
positioning subframe (except those reserved for CRS transmission)
so as to maximize the energy contained in the PRS and to fully
utilize the access point transmit power. In one example, the
resource elements can be comprised within the same subcarrier in
consecutive OFDM symbols for transmitting PRSs. In other examples,
such as that depicted, shifting (diagonal, random, pseudo-random,
or otherwise) can be applied to the subcarriers at each OFDM symbol
to provide a level of diversity and to ensure the channel
estimation has substantially no ambiguity with respect to cyclic
shifts. Moreover, for example, the resource elements selected for
the PRS pattern can have a similar periodicity and similar
structure as the CRS pattern.
[0065] In this or an alternative example, the PRS patterns can be
assigned according to a reuse scheme, which is planned and/or
pseudo-random, to the access points, or cells thereof. In either
case, for example, the PRS patterns can be assigned based at least
in part on an identifier of the access point (e.g., a physical cell
identifier (PCI) of a cell provided by the access point). Moreover,
for example, the PRS sequences assigned to the access points can be
chosen to be Zadoff-Chu sequence, a Walsh sequence, or similar
sequences that ease detection thereof following transmission of the
PRSs. In addition, as described, PRSs can be energy boosted or
spectrally reshaped in the selected resource elements to further
improve hearability (e.g., since the respective access point is
otherwise not transmitting in the slot).
[0066] As depicted, in positioning subframe 300, CRSs are
transmitted as in other subframes for legacy support and/or
identification of a related cell. In addition, data is not
transmitted in the positioning subframe (but can be, for example,
if it is important information such pre-scheduled broadcast
information, etc.). This mitigates interference from surrounding
access points improving hearability of the PRSs, which can enhance
applications such as trilateration or other device location
algorithms. As described, it is to be appreciated that user plane
data can be transmitted by one or more access points in a portion
of the subframe not utilized for transmitting PRSs and/or CRSs
(and/or control data). In addition, PRSs are not embedded within
CRSs so as not to interfere with current applications utilizing
CRSs (e.g., channel estimation and measurement algorithms, etc.).
In this regard, PRSs are provided with increased hearability to
enhance trilateration or similar technologies without interfering
with legacy technologies.
[0067] Turning to FIG. 4, illustrated are example positioning
subframes 400 and 402 in a wireless network transmitted by an
access point with multiple antennas. For example, positioning
subframes 400 and 402 can be OFDM subframes, as described.
Positioning subframes 400 and 402 can be subframes (e.g., a 1 ms or
similar subframe) in an LTE system communicated by an access point
to one or more wireless devices. In an example, positioning
subframe 400 can represent a subframe transmitted with a normal CP,
and positioning subframe 402 can represent a subframe transmitted
with an extended CP. Thus, for example, positioning subframe 400
can comprise 7 OFDM symbols per slot while positioning subframe 402
comprises 6 OFDM symbols per slot. In addition, in an example,
access points in a wireless network (not shown) can blank user plan
data transmissions over positioning subframe 400 and/or 402, as
described herein.
[0068] Positioning subframe 400 comprises two slots 404 and 406. As
described, in a first slot of a given subframe in LTE, control data
can be transmitted over a portion of the resource elements (e.g.,
over one or more initial OFDM symbols). Thus, the OFDM symbols
represented at 408 can be reserved for control data, which can
include CRSs shown as transmitted at resource element 410 and
similarly patterned resource elements within and outside of control
region 408. Additionally, as depicted, resource elements outside of
the control region can also be utilized for transmitting PRSs, such
as resource element 412 and similarly patterned resource elements;
as described, the resource elements can be collectively referred to
as a PRS pattern. In addition, the PRS pattern can be a diagonal or
other shifted pattern over consecutive OFDM symbols. As
illustrated, the PRS pattern utilizes subcarriers over
substantially all OFDM symbols in the special slot(s), except OFDM
symbols in the control region 408, for transmitting the PRSs of an
access point. It is to be appreciated, however, that other patterns
that utilize a different subcarrier (e.g., or one or more shifted
subcarriers) on substantially all OFDM symbols of the special
slot(s) as the resource elements, except in the control region 408,
can be utilized, as described previously. In this regard, resources
elements in slot 404 and slot 406 are reserved for transmitting
PRSs, so long as the resource elements are outside of the control
region 408 and not interfering with CRS resource elements at 410
and similarly patterned CRS resource elements.
[0069] In addition, positioning subframe 402 comprises two slots
414 and 416. As described, in a first slot of a given subframe in
LTE, control data can be transmitted over a portion of the resource
elements (e.g., over one or more initial OFDM symbols). Thus, the
OFDM symbols represented at 418 can be reserved for control data,
which can include CRSs shown as transmitted at resource element 420
and similarly patterned resource elements within and outside of
control region 418. Additionally, as depicted, resource elements
outside of the control region can also be utilized for transmitting
PRSs, such as resource element 422 and similarly patterned resource
elements, which represent the PRS pattern for an access point. In
this regard, resources elements in slot 414 and slot 416 are
reserved for transmitting PRSs, so long as the resource elements
are outside of the control region 418 and do not interfere with CRS
resource elements at 420 and similarly patterned CRS resource
elements.
[0070] Thus, in either example, the PRS patterns do not interfere
with control data transmissions. In addition, as described, by
transmitting PRSs in the resource elements that are otherwise
silenced by the access points, hearability of the PRSs is improved.
As described, resource elements 412 and 422, and similarly
patterned resource elements, can be assigned to the access points
in various ways. For example, the resource elements can be assigned
according to a standard or network specification, which can be
hardcoded in the access point implementation. In this or an
alternative example, the resource elements can be assigned
according to a reuse scheme, which is planned and/or pseudo-random,
to the access points, or cells thereof.
[0071] Where the reuse scheme is planned, in one example, access
points or related cells can be grouped into clusters where each
cluster is assigned common resources for transmitting PRSs. In
either case, for example, the resource elements can be assigned
based at least in part on an identifier of the access point (e.g.,
a PCI of a cell provided by the access point), and/or the like.
Moreover, for example, the sequence transmitted on the resource
elements can be assigned to the access points according to a
sequence, such as a Zadoff-Chu sequence, a Walsh sequence, or
similar sequences that ease detection thereof. In addition, as
described, PRSs can be energy boosted or spectrally reshaped in the
selected resource elements to further improve hearability (e.g.,
since the respective access point is otherwise not transmitting in
the slot).
[0072] As depicted, in positioning subframes 400 and 402, CRSs are
transmitted as in other subframes for legacy support and/or
identification of a related cell. In addition, data is not
transmitted in the positioning subframe, at least not in the
portion utilized to transmit PRSs. This mitigates interference from
surrounding access points improving hearability of the PRSs, which
can enhance applications such as trilateration or other device
location algorithms. As described, it is to be appreciated that
user plane data can be transmitted by one or more access points in
a portion of the subframe not utilized for transmitting PRSs and/or
CRSs (and/or control data). In addition, PRSs are not embedded
within CRSs so as not to interfere with current applications
utilizing CRSs (e.g., channel estimation and measurement
algorithms, etc.). In this regard, PRSs are provided to enhance
trilateration or similar technologies without interfering with
legacy technologies.
[0073] Now referring to FIG. 5, illustrated is an example
positioning subframe 500 in a wireless network. For example,
positioning subframe 500 can be an OFDM subframe, as described.
Positioning subframe 500 can be an MBSFN subframe (e.g., a 1 ms or
similar subframe) in an LTE system communicated by an access point
to one or more wireless devices according to an MBSFN
specification. Positioning subframe 500 comprises two slots 502 and
504. As described, in a first slot of a given subframe in LTE,
control data can be transmitted over a portion of the subframe
(e.g., over one or more initial OFDM symbols) as indicated by
region 506. In this regard, CRSs can be transmitted by various
access points in resource element 508, and similarly patterned
resource elements, in the first slot 502, along with the control
data in region 506.
[0074] Since a positioning subframe 500 is indicated as a MBSFN
subframe, legacy devices can receive the CRSs transmitted in the
control region 506 at resource element 508 and the similarly
patterned resource elements in the same OFDM symbol, and the legacy
devices can ignore the remainder of the positioning subframe 500
since it is an MBSFN subframe. Access points can transmit PRSs in
the remainder of slot 502 and slot 504, indicated at resource
element 510 and similarly patterned resource elements, which
comprises the PRS pattern, and devices equipped to process the PRSs
can receive and process the PRSs to perform trilateration or
similar functionalities. This minimizes confusion of legacy devices
that can be caused by introduction of the PRSs and also improves
hearability thereof by transmitting in slots or related subframes
where transmissions from other access points are substantially
blanked. In addition, as described, utilizing a PRS pattern that
occupies subcarriers in substantially all OFDM symbols, avoiding
control region 506, such as the illustrated diagonal pattern, can
improve channel estimation of the PRSs in the MBSFN subframe.
[0075] As described, resource element 510, and similarly patterned
resource elements, can be assigned to the access points in various
ways for transmitting PRSs. For example, the resource elements can
be assigned according to a standard or network specification, which
can be hardcoded in the access point implementation, a
configuration, and/or the like. In this or an alternative example,
the resource elements can be assigned according to a reuse scheme,
which is planned and/or pseudo-random, to the access points, or
cells thereof. In either case, for example, the resource elements
can be assigned based at least in part on an identifier of the
access point (e.g., a PCI of a cell provided by the access point),
etc. Moreover, for example, the sequence transmitted on the
resource elements can be assigned to the access points according to
a sequence, such as a Zadoff-Chu sequence, a Walsh sequence, or
similar sequences that ease detection thereof. In addition, as
described, PRSs can be energy boosted or spectrally reshaped in the
selected resource elements to further improve hearability (e.g.,
since the respective access point is otherwise not transmitting in
the slot).
[0076] Turning to FIG. 6, example portions of frequency 600, 602,
and 604 are shown that represent PRS resource element selection
schemes. For example, the portions of frequency 600, 602, and 604
can represent an allocation of a plurality of subbands (comprising
a plurality of consecutive resource blocks, for example) in one or
more PRS slots selected or otherwise reserved for transmitting PRSs
by one or more access points in a wireless network. In addition,
though a certain number of subbands are shown in the portions of
frequency 600, 602, and 604, it is to be appreciated that the
portions of frequency 600, 602, and 604 can include more or less
subbands than those depicted.
[0077] According to an example, portion of frequency 600 can
include subbands reserved for PRS/CRS transmissions as well as data
transmissions. In this example, subbands that are numerically
labeled, such as subbands 606, 608, and 610, as well as the
subbands with like numbers, are reserved for transmitting PRS by
first, second and third groups of access points respectively. In
this regard, an access point can be assigned subbands that
correspond to those labeled with the number 1, which includes
subband 606 and the other subbands labeled with the number 1, for
transmitting a PRS in a PRS slot. In addition, disparate access
points can be assigned the subbands corresponding to the numerical
label 2 and 3, such as subbands 608 and 610 respectively and
similarly numbered subbands, for transmitting PRSs.
[0078] The access points can be assigned according to one or more
reuse schemes, in one example, as described. In addition, one or
more access points can transmit data (e.g., physical data shared
channel (PDSCH) data) over the subbands labeled D, such as subband
612 and similarly labeled subbands. Moreover, it is to be
appreciated that additional groups of reserved subbands for
transmitting PRSs can be supported, though only 3 are shown for the
purpose of explanation. In addition, substantially any ordering of
subbands is possible and/or can be modified according to a number
of factors, such as a planned scheme, a reuse scheme, a
pseudo-random allocation, and/or the like. In another example,
subbands for a particular purpose can be contiguous; thus, for
example, subbands with the numeric label 1 can be contiguous
followed by those with the numeric label 2, and so on.
[0079] In another example, portions of frequency 602 and 604
illustrate an example where bandwidth of a carrier is larger than
that required for time resolution capability. In this regard,
portions of frequency 602 and 604 can include guard band 614
between contiguous subbands reserved for similar types of
transmissions. Thus, as shown for example, portion of frequency 602
can include no data transmission subbands, rather only subbands for
transmitting PRS/CRS, such as subbands represented by numeric label
1, including subband 606, subbands represented by numeric label 2,
including subband 608, and subbands represented by numeric label 3,
including subband 610. The guard band 614, and similar subbands
with no label, separate the subbands to facilitate independent
reception of the subbands without significant interference leaked
from the respective subband groups.
[0080] Portion of frequency 604 can include multiple groups of
subbands reserved for data, such as subband 612 and the other
subbands labeled D, as well as one or more subbands for
transmitting PRS/CRS, such as subband 606 and other subbands
labeled 1. Similarly, the subband groups in portion of frequency
604 can be separated by guard band 614 to facilitate independent
reception of signals transmitted in the subband group since the
guard band provides a separation mitigating leakage between
frequency bands (and thus interference). It is to be appreciated
that additional configurations are possible; portions of frequency
600, 602, and 604 are but 3 examples of allocating subbands in
slots selected for transmitting PRSs to mitigate interference among
the PRSs and/or data transmitted in the selected slots.
[0081] Referring next to FIG. 7, a communications apparatus 700
that can participate in a wireless communications network is
illustrated. The communications apparatus 700 can be an access
point, a mobile device, a portion thereof, or substantially any
device that receives communications in a wireless network. The
communications apparatus 700 can include a positioning subframe
selecting component 702 that determines one or more subframes to be
a subframe for transmitting CRSs, an MBSFN subframe determining
component 704 that discerns one or more subframes to be an MBSFN
subframe, an MBSFN subframe specifying component 706 that can
indicate a subframe as being an MBSFN subframe, and a transmitting
component 708 that can transmit data and/or CRSs in one or more
subframes.
[0082] According to an example, positioning subframe selecting
component 702 can select one or more subframes for transmitting
CRSs according to a network specification, configuration,
hardcoding, etc., or according to a fixed or pseudo-random patter,
and/or the like, as described. In this regard, transmitting
component 708 can typically blank data transmissions and transmit
CRSs in the selected positioning subframe. In addition, however,
MBSFN subframe determining component 704 can select one or more of
the positioning subframes to be indicated as an MBSFN subframe to
mitigate CRS transmission in the MBSFN indicated subframe. This
mitigates interference to other apparatuses (not shown) that
transmit CRSs in the subframe, which provides a level of reuse for
CRS transmission. In this way, MBSFN subframe determining component
704 can select positioning subframes to be MBSFN subframes
according to one or more factors to increase reuse. For example,
MBSFN subframe determining component 704 can receive an indication
of a subframe to be MBSFN from an underlying wireless network (not
shown), determine the subframe according to a planned or
pseudo-random pattern (which can be received according to a
specification, configuration, hardcoding, etc.), and/or the like.
MBSFN subframe specifying component 706 can indicate the subframe
as MBSFN allowing receiving devices to receive the other CRSs
without attempting to decode CRSs from communications apparatus
700, for example. In addition, transmitting component 708 can blank
data transmissions and transmit CRSs in positioning subframes
selected by positioning subframe selecting component 702 that are
not determined to be MBSFN subframes by MBSFM subframe determining
component 704.
[0083] In another example, MBSFN subframe determining component 704
can discern substantially all subframes selected as positioning
subframes by positioning subframe selecting component 702 to be
MBSFN subframes to blank CRS transmission over the subframes. In
this regard, transmitting component 708, and similar components of
other apparatuses, can select MBSFN subframes for transmitting a
CRS-like waveform, and blanking data transmissions, according to a
planned or pseudo-random pattern, and/or the like. This increases a
reuse factor for the CRSs (or similar waveforms) improving
hearability thereof by some devices (e.g., LTE-A devices) over a
plurality of subframes, while other devices (e.g., LTE release 8
devices) do not process the CRS-like waveforms as CRSs are not
expected in MBSFN subframes, as described.
[0084] Referring now to FIGS. 8-11, methodologies that can be
performed in accordance with various aspects set forth herein are
illustrated. While, for purposes of simplicity of explanation, the
methodologies are shown and described as a series of acts, it is to
be understood and appreciated that the methodologies are not
limited by the order of acts, as some acts can, in accordance with
one or more aspects, occur in different orders and/or concurrently
with other acts from that shown and described herein. For example,
those skilled in the art will understand and appreciate that a
methodology could alternatively be represented as a series of
interrelated states or events, such as in a state diagram.
Moreover, not all illustrated acts may be required to implement a
methodology in accordance with one or more aspects.
[0085] With reference to FIG. 8, illustrated is an example
methodology 800 for transmitting PRS in a portion of a positioning
subframe. At 802, a positioning subframe for transmitting PRS can
be determined. In one example, this can include determining a
portion of the positioning subframe, such as a slot or portion
thereof, allocated for PRS transmission, which can be determined
based on a standard, network specification, configuration,
hardcoding, and/or the like. The positioning subframe, as
described, can include a plurality of resource elements, a portion
of which can be reserved for CRS and/or control data transmissions.
At 804, one or more resource elements in the positioning subframe,
not allocated for CRS transmission, can be selected for
transmitting a PRS. As described, the one or more resource elements
can be selected according to a planned or pseudo-random selection
function, which can be based on a cell identifier, etc.
[0086] In addition, the one or more resource elements can be
excluded from those allocated for transmitting control data. In
this regard, legacy devices can still receive CRSs and control data
to reduce impact of introducing PRS transmissions. In another
example, the one or more resource elements can be selected from
within a subband of the positioning subframe, where the subband is
allocated for transmitting PRSs. As described previously, the
subband can be adjacent to additional subbands allocated for
transmitting disparate PRSs, user plane data, etc., adjacent to
guard band, and/or the like. At 806, the PRS can be transmitted in
the one or more resource elements. In one example, a transmit
diversity scheme can be applied to the PRS to further reduce impact
of the PRSs on legacy devices and to ensure the channel estimation
of the PRS has substantially no ambiguity with respect to cyclic
shifts. In addition, the PRS can be transmitted utilizing
substantially all available transmission power.
[0087] Turning to FIG. 9, an example methodology 900 is illustrated
that facilitates transmitting PRSs in a backward compatible manner.
At 902, a positioning subframe for transmitting PRS can be
determined. In one example, this can include determining a portion
of the positioning subframe, such as a slot or portion thereof,
allocated for PRS transmission. The positioning subframe, as
described, can include a plurality of resource elements, a portion
of which can be reserved for CRS and/or control data transmissions.
At 904, one or more resource elements in the positioning subframe,
not allocated for CRS transmission, can be selected for
transmitting a PRS. As described, the one or more resource elements
can be selected according to a planned or pseudo-random selection
function, which can be based on a cell identifier, etc. At 906, it
can be indicated that the positioning subframe is an MBSFN
subframe. In this regard, legacy devices receiving the positioning
subframe can ignore the portion not reserved for control data, and
thus will not receive the PRSs. This mitigates potential confusion
to the legacy devices caused by introducing the PRSs. At 908, the
PRS can be transmitted in the one or more resource elements, as
described.
[0088] Turning to FIG. 10, an example methodology 1000 is
illustrated that facilitates indicating positioning subframes as
MBSFN subframes to control CRS transmission in the subframes. At
1002, one or more subframes can be selected as positioning
subframes for blanking data transmissions. As described, the
subframes can be selected according to a pseudo-random or planned
pattern, which can be received from a network device, determined
according to a network specification, configuration, or hardcoding,
etc. At 1004, one or more of the positioning subframes can be
indicated as MBSFN subframes to further blank CRS transmissions. As
described, positioning subframes to be indicated as MBSFN subframes
can be selected according to planned, pseudo-random, or other
pattern to increase reuse of CRSs among multiple access points. In
addition, the pattern can be defined in a network specification,
configuration, hardcoding, etc. It is to be appreciated, in an
alternative example, that all positioning subframes can be
indicated as MBSFN subframes. Subsequently, MBSFN subframes can be
selected for transmitting CRS, as described above.
[0089] Turning to FIG. 11, an example methodology 1100 is
illustrated that facilitates indicating positioning subframes as
MBSFN subframes to control CRS transmission in the subframes. At
1102, one or more subframes can be selected as positioning
subframes for blanking data transmissions. As described, the
subframes can be selected according to a pseudo-random or planned
pattern, which can be received from a network device, determined
according to a network specification, configuration, or hardcoding,
etc. At 1104, substantially all of the positioning subframes can be
indicated as MBSFN subframes. At 1106, CRS-like waveforms can be
transmitted in one or more of the MBSFN subframes. As described,
the one or more MBSFN subframes over which to transmit the CRS-like
waveforms can be selected according to planned, pseudo-random, or
other pattern to increase reuse of CRSs (or CRS-like waveforms)
among multiple access points. In addition, the pattern can be
defined in a network specification, configuration, hardcoding,
etc.
[0090] It will be appreciated that, in accordance with one or more
aspects described herein, inferences can be made regarding
determining subframes, slots, subbands, resource blocks, resource
elements, etc., for transmitting PRSs, and/or the like. As used
herein, the term to "infer" or "inference" refers generally to the
process of reasoning about or inferring states of the system,
environment, and/or user from a set of observations as captured via
events and/or data. Inference can be employed to identify a
specific context or action, or can generate a probability
distribution over states, for example. The inference can be
probabilistic--that is, the computation of a probability
distribution over states of interest based on a consideration of
data and events. Inference can also refer to techniques employed
for composing higher-level events from a set of events and/or data.
Such inference results in the construction of new events or actions
from a set of observed events and/or stored event data, whether or
not the events are correlated in close temporal proximity, and
whether the events and data come from one or several event and data
sources.
[0091] With reference to FIG. 12, illustrated is a system 1200 that
transmits PRSs in positioning subframes to improve hearability
thereof. For example, system 1200 can reside at least partially
within a base station, mobile device, etc. It is to be appreciated
that system 1200 is represented as including functional blocks,
which can be functional blocks that represent functions implemented
by a processor, software, or combination thereof (e.g., firmware).
System 1200 includes a logical grouping 1202 of electrical
components that can act in conjunction. For instance, logical
grouping 1202 can include an electrical component for determining a
positioning subframe configured for transmitting PRSs 1204. As
described, this can be determined from a standard, network
specification, configuration, hardcoding, and/or the like. In
addition, electrical component 1204 can determine a portion of the
positioning subframe allocated for transmitting PRSs, such as a
slot, subband, and/or the like.
[0092] Further, logical grouping 1202 can comprise an electrical
component for selecting one or more resource elements in the
positioning subframe, excluding a set of resource elements
allocated for transmitting CRSs, for transmitting a PRS 1206. As
described, this can include selecting the resource elements
according to a planned or pseudo-random function, which can be
based on an identifier of a cell provided by system 1200, or other
constant or variable, etc. In addition, electrical component 1206
can select the one or more resource elements according to a PRS
pattern, as described previously (according to the planned or
pseudo-random function or otherwise), which can be a diagonal
pattern or substantially any pattern that selects different
resource elements from consecutive OFDM symbols in a positioning
subframe for transmitting PRSs.
[0093] Moreover, logical grouping 1202 includes an electrical
component for transmitting the PRS in the one or more resource
elements 1208. In one example, electrical component 1208 can
transmit the PRS with substantially all available transmit power.
In addition, logical grouping 1202 can include an electrical
component for applying a transmit diversity scheme to the PRS 1210.
This can include a PVS, CDD, and/or the like to ensure the channel
estimation of the PRS has substantially no ambiguity with respect
to cyclic shifts. Additionally, system 1200 can include a memory
1212 that retains instructions for executing functions associated
with electrical components 1204, 1206, 1208, and 1210. While shown
as being external to memory 1212, it is to be understood that one
or more of electrical components 1204, 1206, 1208, and 1210 can
exist within memory 1212.
[0094] With reference to FIG. 13, illustrated is a system 1300 that
indicates one or more positioning subframes as an MBSFN subframe to
improve hearability of CRSs. For example, system 1300 can reside at
least partially within a base station, mobile device, etc. It is to
be appreciated that system 1300 is represented as including
functional blocks, which can be functional blocks that represent
functions implemented by a processor, software, or combination
thereof (e.g., firmware). System 1300 includes a logical grouping
1302 of electrical components that can act in conjunction. For
instance, logical grouping 1302 can include an electrical component
for selecting one or more subframes as one or more positioning
subframes for blanking data transmissions 1304. As described, the
positioning subframes can be selected according to a planned,
pseudo-random, or other pattern that can be determined or received
from a standard, network specification, configuration, hardcoding,
and/or the like.
[0095] Further, logical grouping 1302 can comprise an electrical
component for determining the one or more positioning subframes as
one or more MBSFN subframes 1306. As described, this can include
selecting the MBSFN subframes according to a planned,
pseudo-random, or other pattern that increases reuse of CRSs
transmitted in the non-MBSFN positioning subframes. Moreover,
logical grouping 1302 includes an electrical component for
indicating the one or more MBSFN subframes as MBSFN subframes 1308.
Thus, receiving devices can appropriately process signals received
in the subframes. In addition, logical grouping 1302 can include an
electrical component for transmitting CRS-like waveforms in at
least one of the one or more MBSFN subframes 1310. When electrical
component 1310 is present, substantially all positioning subframes
can be indicated as MBSFN subframes, as described, allowing
electrical component 1310 to select subframes for transmitting
CRS-like waveforms to improve hearability thereof to devices able
to receive and process such waveforms. Additionally, system 1300
can include a memory 1312 that retains instructions for executing
functions associated with electrical components 1304, 1306, 1308,
and 1310. While shown as being external to memory 1312, it is to be
understood that one or more of electrical components 1304, 1306,
1308, and 1310 can exist within memory 1312.
[0096] FIG. 14 is a block diagram of a system 1400 that can be
utilized to implement various aspects of the functionality
described herein. In one example, system 1400 includes a base
station or eNB 1402. As illustrated, eNB 1402 can receive signal(s)
from one or more UEs 1404 via one or more receive (Rx) antennas
1406 and transmit to the one or more UEs 1404 via one or more
transmit (Tx) antennas 1408. Additionally, eNB 1402 can comprise a
receiver 1410 that receives information from receive antenna(s)
1406. In one example, the receiver 1410 can be operatively
associated with a demodulator (Demod) 1412 that demodulates
received information. Demodulated symbols can then be analyzed by a
processor 1414. Processor 1414 can be coupled to memory 1416, which
can store information related to code clusters, access terminal
assignments, lookup tables related thereto, unique scrambling
sequences, and/or other suitable types of information. In one
example, eNB 1402 can employ processor 1414 to perform
methodologies 800, 900, 1000, 1100, and/or other similar and
appropriate methodologies. eNB 1402 can also include a modulator
1418 that can multiplex a signal for transmission by a transmitter
1420 through transmit antenna(s) 1408.
[0097] FIG. 15 is a block diagram of another system 1500 that can
be utilized to implement various aspects of the functionality
described herein. In one example, system 1500 includes a mobile
terminal 1502. As illustrated, mobile terminal 1502 can receive
signal(s) from one or more base stations 1504 and transmit to the
one or more base stations 1504 via one or more antennas 1508.
Additionally, mobile terminal 1502 can comprise a receiver 1510
that receives information from antenna(s) 1508. In one example,
receiver 1510 can be operatively associated with a demodulator
(Demod) 1512 that demodulates received information. Demodulated
symbols can then be analyzed by a processor 1514. Processor 1514
can be coupled to memory 1516, which can store data and/or program
codes related to mobile terminal 1502. Additionally, mobile
terminal 1502 can employ processor 1514 to perform methodologies
800, 900, 1000, 1100, and/or other similar and appropriate
methodologies. Mobile terminal 1502 can also employ one or more
components described in previous figures to effectuate the
described functionality; in one example, the components can be
implemented by the processor 1514. Mobile terminal 1502 can also
include a modulator 1518 that can multiplex a signal for
transmission by a transmitter 1520 through antenna(s) 1508.
[0098] Referring now to FIG. 16, an illustration of a wireless
multiple-access communication system is provided in accordance with
various aspects. In one example, an access point 1600 (AP) includes
multiple antenna groups. As illustrated in FIG. 16, one antenna
group can include antennas 1604 and 1606, another can include
antennas 1608 and 1610, and another can include antennas 1612 and
1614. While only two antennas are shown in FIG. 16 for each antenna
group, it should be appreciated that more or fewer antennas may be
utilized for each antenna group. In another example, an access
terminal 1616 can be in communication with antennas 1612 and 1614,
where antennas 1612 and 1614 transmit information to access
terminal 1616 over forward link 1620 and receive information from
access terminal 1616 over reverse link 1618. Additionally and/or
alternatively, access terminal 1622 can be in communication with
antennas 1606 and 1608, where antennas 1606 and 1608 transmit
information to access terminal 1622 over forward link 1626 and
receive information from access terminal 1622 over reverse link
1624. In a frequency division duplex system, communication links
1618, 1620, 1624 and 1626 can use different frequency for
communication. For example, forward link 1620 may use a different
frequency then that used by reverse link 1618.
[0099] Each group of antennas and/or the area in which they are
designed to communicate can be referred to as a sector of the
access point. In accordance with one aspect, antenna groups can be
designed to communicate to access terminals in a sector of areas
covered by access point 1600. In communication over forward links
1620 and 1626, the transmitting antennas of access point 1600 can
utilize beamforming in order to improve the signal-to-noise ratio
of forward links for the different access terminals 1616 and 1622.
Also, an access point using beamforming to transmit to access
terminals scattered randomly through its coverage causes less
interference to access terminals in neighboring cells than an
access point transmitting through a single antenna to all its
access terminals.
[0100] An access point, e.g., access point 1600, can be a fixed
station used for communicating with terminals and can also be
referred to as a base station, an eNB, an access network, and/or
other suitable terminology. In addition, an access terminal, e.g.,
an access terminal 1616 or 1622, can also be referred to as a
mobile terminal, user equipment, a wireless communication device, a
terminal, a wireless terminal, and/or other appropriate
terminology.
[0101] Referring now to FIG. 17, a block diagram illustrating an
example wireless communication system 1700 in which various aspects
described herein can function is provided. In one example, system
1700 is a multiple-input multiple-output (MIMO) system that
includes a transmitter system 1710 and a receiver system 1750. It
should be appreciated, however, that transmitter system 1710 and/or
receiver system 1750 could also be applied to a multi-input
single-output system wherein, for example, multiple transmit
antennas (e.g., on a base station), can transmit one or more symbol
streams to a single antenna device (e.g., a mobile station).
Additionally, it should be appreciated that aspects of transmitter
system 1710 and/or receiver system 1750 described herein could be
utilized in connection with a single output to single input antenna
system.
[0102] In accordance with one aspect, traffic data for a number of
data streams are provided at transmitter system 1710 from a data
source 1712 to a transmit (TX) data processor 1714. In one example,
each data stream can then be transmitted via a respective transmit
antenna 1724. Additionally, TX data processor 1714 can format,
encode, and interleave traffic data for each data stream based on a
particular coding scheme selected for each respective data stream
in order to provide coded data. In one example, the coded data for
each data stream can then be multiplexed with pilot data using OFDM
techniques. The pilot data can be, for example, a known data
pattern that is processed in a known manner. Further, the pilot
data can be used at receiver system 1750 to estimate channel
response. Back at transmitter system 1710, the multiplexed pilot
and coded data for each data stream can be modulated (i.e., symbol
mapped) based on a particular modulation scheme (e.g., BPSK, QSPK,
M-PSK, or M-QAM) selected for each respective data stream in order
to provide modulation symbols. In one example, data rate, coding,
and modulation for each data stream can be determined by
instructions performed on and/or provided by processor 1730.
[0103] Next, modulation symbols for all data streams can be
provided to a TX processor 1720, which can further process the
modulation symbols (e.g., for OFDM). TX MIMO processor 1720 can
then provides N.sub.T modulation symbol streams to N.sub.T
transceivers 1722a through 1722t. In one example, each transceiver
1722 can receive and process a respective symbol stream to provide
one or more analog signals. Each transceiver 1722 can then further
condition (e.g., amplify, filter, and upconvert) the analog signals
to provide a modulated signal suitable for transmission over a MIMO
channel. Accordingly, N.sub.T modulated signals from transceivers
1722a through 1722t can then be transmitted from N.sub.T antennas
1724a through 1724t, respectively.
[0104] In accordance with another aspect, the transmitted modulated
signals can be received at receiver system 1750 by N.sub.R antennas
1752a through 1752r. The received signal from each antenna 1752 can
then be provided to respective transceivers 1754. In one example,
each transceiver 1754 can condition (e.g., filter, amplify, and
downconvert) a respective received signal, digitize the conditioned
signal to provide samples, and then processes the samples to
provide a corresponding "received" symbol stream. An RX MIMO/data
processor 1760 can then receive and process the N.sub.R received
symbol streams from N.sub.R transceivers 1754 based on a particular
receiver processing technique to provide N.sub.T "detected" symbol
streams. In one example, each detected symbol stream can include
symbols that are estimates of the modulation symbols transmitted
for the corresponding data stream. RX processor 1760 can then
process each symbol stream at least in part by demodulating,
deinterleaving, and decoding each detected symbol stream to recover
traffic data for a corresponding data stream. Thus, the processing
by RX processor 1760 can be complementary to that performed by TX
MIMO processor 1720 and TX data processor 1718 at transmitter
system 1710. RX processor 1760 can additionally provide processed
symbol streams to a data sink 1764.
[0105] In accordance with one aspect, the channel response estimate
generated by RX processor 1760 can be used to perform space/time
processing at the receiver, adjust power levels, change modulation
rates or schemes, and/or other appropriate actions. Additionally,
RX processor 1760 can further estimate channel characteristics such
as, for example, signal-to-noise-and-interference ratios (SNRs) of
the detected symbol streams. RX processor 1760 can then provide
estimated channel characteristics to a processor 1770. In one
example, RX processor 1760 and/or processor 1770 can further derive
an estimate of the "operating" SNR for the system. Processor 1770
can then provide channel state information (CSI), which can
comprise information regarding the communication link and/or the
received data stream. This information can include, for example,
the operating SNR. The CSI can then be processed by a TX data
processor 1718, modulated by a modulator 1780, conditioned by
transceivers 1754a through 1754r, and transmitted back to
transmitter system 1710. In addition, a data source 1716 at
receiver system 1750 can provide additional data to be processed by
TX data processor 1718.
[0106] Back at transmitter system 1710, the modulated signals from
receiver system 1750 can then be received by antennas 1724,
conditioned by transceivers 1722, demodulated by a demodulator
1740, and processed by a RX data processor 1742 to recover the CSI
reported by receiver system 1750. In one example, the reported CSI
can then be provided to processor 1730 and used to determine data
rates as well as coding and modulation schemes to be used for one
or more data streams. The determined coding and modulation schemes
can then be provided to transceivers 1722 for quantization and/or
use in later transmissions to receiver system 1750. Additionally
and/or alternatively, the reported CSI can be used by processor
1730 to generate various controls for TX data processor 1714 and TX
MIMO processor 1720. In another example, CSI and/or other
information processed by RX data processor 1742 can be provided to
a data sink 1744.
[0107] In one example, processor 1730 at transmitter system 1710
and processor 1770 at receiver system 1750 direct operation at
their respective systems. Additionally, memory 1732 at transmitter
system 1710 and memory 1772 at receiver system 1750 can provide
storage for program codes and data used by processors 1730 and
1770, respectively. Further, at receiver system 1750, various
processing techniques can be used to process the N.sub.R received
signals to detect the N.sub.T transmitted symbol streams. These
receiver processing techniques can include spatial and space-time
receiver processing techniques, which can also be referred to as
equalization techniques, and/or "successive nulling/equalization
and interference cancellation" receiver processing techniques,
which can also be referred to as "successive interference
cancellation" or "successive cancellation" receiver processing
techniques.
[0108] It is to be understood that the aspects described herein can
be implemented by hardware, software, firmware, middleware,
microcode, or any combination thereof. When the systems and/or
methods are implemented in software, firmware, middleware or
microcode, program code or code segments, they can be stored in a
machine-readable medium, such as a storage component. A code
segment can represent a procedure, a function, a subprogram, a
program, a routine, a subroutine, a module, a software package, a
class, or any combination of instructions, data structures, or
program statements. A code segment can be coupled to another code
segment or a hardware circuit by passing and/or receiving
information, data, arguments, parameters, or memory contents.
Information, arguments, parameters, data, etc. can be passed,
forwarded, or transmitted using any suitable means including memory
sharing, message passing, token passing, network transmission,
etc.
[0109] For a software implementation, the techniques described
herein can be implemented with modules (e.g., procedures,
functions, and so on) that perform the functions described herein.
The software codes can be stored in memory units and executed by
processors. The memory unit can be implemented within the processor
or external to the processor, in which case it can be
communicatively coupled to the processor via various means as is
known in the art.
[0110] What has been described above includes examples of one or
more aspects. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the aforementioned aspects, but one of ordinary skill
in the art can recognize that many further combinations and
permutations of various aspects are possible. Accordingly, the
described aspects are intended to embrace all such alterations,
modifications and variations that fall within the spirit and scope
of the appended claims. Furthermore, to the extent that the term
"includes" is used in either the detailed description or the
claims, such term is intended to be inclusive in a manner similar
to the term "comprising" as "comprising" is interpreted when
employed as a transitional word in a claim. Furthermore, the term
"or" as used in either the detailed description or the claims is
meant to be a "non-exclusive or."
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